1. Field of the Invention
The present invention relates to macroporous monolithic materials, in particular to carbon monoliths and to ceramic monoliths comprising an M2 (Macroporous/Microporous) hierarchical porous structure, to a process for the preparation thereof and to the use thereof, in particular in the manufacture of hydrogen purifiers, supercapacitors or electrodes or alternatively in carrying out chemical reactions catalyzed in a heterogeneous phase.
2. Description of Related Art
The materials provided in the form of porous carbon monoliths constitute materials of choice for numerous applications, such as the purification of water and air, adsorption, heterogeneous-phase catalysis, the manufacture of electrodes and the storage of energy, due to their high specific surface, their high pore volume, their insensitivity to the surrounding chemical reactions and their excellent mechanical properties.
These materials comprise a high specific surface and a hierarchical structure, that is to say a cellular structure generally exhibiting a double porosity. They exhibit in particular a mesoporous structure in which the mean pore diameter varies from the order of 2 to 10 nm.
They can be prepared according to two main families of processes.
The first main family of processes uses soft templates and corresponds to the soft templating methods, i.e. to the methods employing organic/organic interactions between a thermopolymerizable polymer (generally carbon precursor) and certain block copolymers of non-ionic polymer type, such as the products sold under the trade names Pluronic® P123 or F127 by BASF, which are used as modeling agent, in order to directly obtain a porous carbonaceous material after carbonization under an inert atmosphere at 350° C. and pyrolysis (Meng Y. et al., Angew. Chem. Int. Ed., 2005, 44, 2).
The second main family of processes uses rigid templates and corresponds to the hard templating or exotemplating methods, i.e. to the methods in which a mesoporous solid template is impregnated with a solution of a precursor of the final material which it is desired to obtain (for example carbon precursor), before being carbonized under a nonoxidizing atmosphere.
The invention which will be described below comes within the scope of the hard templating methods.
More specifically, the hard templating methods employ templates which can be composed in particular of particles of mesoporous silica, of alumina membranes, of zeolites, and the like. In particular, it is known, for example from the paper by K. P. Gierszal et al. (New Journal of Chemistry, 2008, 32, 981-993), to prepare mesoporous carbon monoliths according to a method using matrices formed of mesoporous silica of MCM-48 and KIT-6 type having a cubic 3D structure. According to this process, the silica matrices, in the form of powders, are first of all impregnated with a solution of a carbon precursor, which precursor is subsequently crosslinked within the matrices, and then the matrices are carbonized. The carbonaceous material is finally obtained after removal of the silica template by a treatment with acid. It is provided in the form of a mesoporous material, the pores of which have a mean diameter of between 3 and 5 nm approximately and the pore network of which has a structure which corresponds substantially to the negative of the pore network of the template used. Furthermore, a description has also been given, in particular by Alvarez S. at al. (Advanced Engineering Materials, 2004, 6(11), 897-899), of the preparation of carbon monoliths comprising a macro/mesoporous network by impregnation of a solid template formed of meso/macroporous silica with a solution of a carbon precursor, such as furfuryl alcohol, which is subsequently polymerized within the template before the latter is removed, for example by an acid treatment. The carbon monoliths obtained according to the method described by Alvarez S. et al. comprise a macroporous network which is the positive replica of the macroporous network of the silica template used and a mesoporous network which corresponds to the negative of the mesoporous network of the silica template used.
There currently exists no hard-templating process which allows access to materials comprising a hierarchical porous network comprising a macroporous network, which is the exact replica of the macroporous network of the silica template used, and a microporous network, while being devoid of a mesoporous network.